A series of hydroxypropyl cellulose/polyurethane blends (PU_HPC 20/80, PU_HPC 50/50 and PU_HPC 80/20) were investigated by FT-IR spectroscopy after exposure to simulated ageing conditions (UV irradiation, 40 °C and 60% humidity) for 600 h. The degree of structural organization was analyzed through quantitative determination of the crystallinity indexes: total crystallinity index (TCI), lateral order index (LOI) and the hydrogen bond intensity (HBI), as well as by the evolution of the "ordered",

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... "disordered" and "free" areas in the carbonyl (1600-1800 cm-1) spectral region. The accelerated weathering conditions determined structural modification in the PU_HPC blends in correlation with their composition and the exposure time, both polymeric components being affected by the hydrolysis and oxidation processes.